Diesel-powered vehicles such as the commercial tracks and the like are frequently operated in excess of the safe and/or optimum conditions of engine and vehicle speed. The resistance of the operators of these vehicles to comply with posted and accepted safe maximum speed limits will ultimately result in provision for an automatic, self-contained unit limiting vehicle speed. Such a control system is desirable not only for safety, but, also to prevent abuse of the vehicle and avoid premature engine and/or vehicle overhauls.
The problems and expenses of installation of such control systems becomes enormous if applied to the millions of trucks which are presently in service. Any system to be effective, therefore, must provide a very facile and inexpensive retrofitting of existing vehicles and, in particular, must not involve any substantial engine or vehicle modifications.
The typical diesel-powered vehicle is not a simple vehicle for installing a retrofit speed governing device since many of such vehicles have engine compression braking whereby the exhaust valves of the engine are opened during the power stroke of the engine in the fuel shut-off or shut down mode so that the engine functions as an air compressor. Accordingly, any attempted utilization of the shut down operation of the diesel engine for automatically responding to excessive vehicle and/or engine speed results in a very jerky and abrupt cycling of the vehicle, rendering the vehicle entirely unsuited for use.